A roof collapse has injured at least 17 people and shut down the nations' busiest border crossing. 

Three people have been taken to hospitals after a portion of the roof in the Secondary Inspection area collapsed around 10:45 a.m. Wednesday morning at the crossing connecting San Diego and Tijuana, Mexico.

Fifteen cars were in the Secondary Inspection area when a large wooden platform collapsed, San Diego Fire spokesperson Maurice Luque told NBC San Diego.

U.S. Customs and Border Protection says it does not know how serious the injuries are. Fourteen other people who were injured were treated at the scene.

All 24 of the border crossing's lanes entering the U.S. are now closed.

Authorities says all U.S.-bound vehicles and pedestrians are being directed to San Diego's other border crossing about five miles away. They has no estimate of when the San Ysidro crossing will re-open.

The Associated Press contributed to this report.